1. Field of the Invention
This invention relates to a stabilized superconducting wire having a stabilizing material section disposed around a multicore section and particularly to a stabilized superconducting wire having a barrier layer (hereinafter referred to as diffusion barrier layer) which is improved to prevent elements in an alloy matrix from diffusing into a stabilizing material section to contaminate the latter.
2. Description of the Related Art
In the application of superconduction to nuclear fusion, energy storage, analytic NMR magnets, etc., there is a need for a superconducting wire which will exhibit superior characteristics in high magnetic fields. For practical superconducting wires for use in high magnetic fields, such superconducting compound materials as Nb.sub.3 Sn and V.sub.3 Ga are used. These superconducting compound materials are produced by the so-called "bronze process." In the case of Nb.sub.3 Sn, an Nb multicore section in a Cu-Sn alloy matrix is subjected to a heat treatment which brings about a diffusion reaction between the Nb and the Sn in the matrix, thereby forming Nb.sub.3 Sn. In the case of V.sub.3 Ga, a V multicore section in a Cu-Ga alloy matrix is subjected to a heat treatment which brings about a diffusion reaction between the V and the Ga in the matrix, thereby forming V.sub.3 Ga.
FIG. 1 is a perspective view for explaining a conventional stabilized superconducting wire using a superconducting compound material. In FIG. 1, a stabilizing material section 4 is positioned around a multicore section 1 composed of a number of filaments 11 of superconducting compound material placed in an alloy matrix. Disposed between said stabilized material section 4 and the multicore section 1 is a diffusion barrier layer 6. Cu is generally used for the stabilizing material section 4. A desirable material for the diffusion barrier layer is one which has satisfactory plastic workability not to produce such drawbacks as breakage during wire drawing process and which hardly diffuses into the stabilizing material section. Heretofore, such metals as Nb and Ta have been used as materials which meet these requirements.
However, since Nb and Ta are expensive, the use of these metals as a diffusion barrier layer brings about a corresponding problem in that the cost of the resulting superconducting wire is high. Thus, there has been a need for an inexpensive material for diffusion barrier layers.
In the case where Nb is used as a diffusion barrier layer and Nb.sub.3 Sn as a superconducting compound material, there has been the problem of a large coupling loss occurring in the multicore. This is caused by the Sn in the alloy matrix diffusing to the Nb in the diffusion barrier layer to react with the Nb during heat treatment, thereby forming a cylindrical Nb.sub.3 Sn superconducting layer in the interface between the alloy matrix and the diffusion barrier layer. When subjected to a varying magnetic field, this Nb.sub.3 Sn superconducting layer produces a large hysteresis loss and also produces a large coupling loss in the multicore; as a result, it drastically decreases the efficiency of the superconducting wire.